Fibre Optic Microprobes and Measurement of the Light Microenvironment within Plant Tissues

From a physical standpoint, plants are extremely complicated optical systems and the light regime within their tissues is determined by a number of processes such as absorption, light scattering, and the focusing of light by epidermal cells. Although various mathematical approaches have been applied to describe the light environment within plant tissues, it is difficult to correct for all the optical phenomena and only simplified models have been developed. Considering this and the fact that optical properties vary widely among plants, it is desirable to be able to measure experimentally the light that exists within cells and tissues and to be able to quantify the amount of light, its spectral quality, and direction of travel. Fiber optic microprobes have been developed with this goal in mind and numerous improvements have occurred since the technique was originally described. The idea behind this technique is relatively simple: optical fiber can be heated and stretched to a fine tip, which can be sealed optically to allow light entry only into the extreme tip. This chapter summarizes the current status of the fiber optic microprobe technique. It describes: (a) how the probes are fabricated, (b) associated instrumentation, (c) measurements obtained with the probe, and (d) special problems in signal interpretation.